key: cord-022381-x15ki4xv
authors: Goldblum, Randall M.; Goldman, Armond S.
title: Immunological Components of Milk: Formation and Function
date: 2012-12-02
journal: Handbook of Mucosal Immunology
DOI: 10.1016/b978-0-12-524730-6.50056-7
sha: 
doc_id: 22381
cord_uid: x15ki4xv

nan

tion of milk fat. The substrate for milk fat synthesis derives from two sources. Fatty acids are synthesized from glucose by mammary alveolar cells that contain fatty acid synthetase. These fatty acids have somewhat shorter chain lengths (10-16 carbons) than those synthesized in adipose tissue because of the presence of a mammary gland-specific enzyme called thioesterase II. In addition, plasma triacylglycerols are cleaved within the mammary gland by the enzyme lipoprotein lipase. The resulting fatty acids are transported into the mammary alveolar cells, where they are reesterified with glycol to make the neutral fat molecules that coalesce to form milk fat globules. Alveolar cells have a columnar shape with copious endoplasmic reticulum surrounding the nucleus in the basal region. During milk secretion, the Golgi apparatus and secretory vesicles become more numerous toward the apical pole. Abundant cytoplasmic lipid droplets enlarge as they move toward the luminal end of the cell. As they press into the apical plasma membrane, the droplets are released into the milk as membrane-bound milk fat globules (Moyer-Mileur and Chan, 1989) . Other globules that are formed during this process contain fewer lipids but larger amounts of other cytoplasmic constituents (Patton and Huston, 1985) .

The third pathway transports certain small molecules including sodium, potassium, chloride, and glucose across the apical membrane of the cell. The secretion of the monovalent ions is effected by the electrical gradient across this membrane.

The fourth pathway transfers proteins and possible other substances from the interstitial space to the lumen using receptors and intracellular vesicles. This mechanism will be considered in the description of the formation of secretory Ig A (SIgA) in milk via polymeric immunoglobulin receptors.

Finally, in addition to soluble components, certain cells and cellular membranes enter human colostrum and milk. Epithelial cells or their membranes are shed directly into milk. Most B cells that home to the mammary gland remain sessile, whereas many T cells, macrophages, and neutrophils that have entered the lamina propria pass through the intercellular junctions of alveolar cells into the milk (Brandtzaeg, 1983) . The mechanisms that attract the leukocytes to the mammary gland and trigger the migration of those cells into the milk are considered in a subsequent section.

Milk secretions are stored in the alveoli and small ducts until they are ejected during nursing. Epithelial cells of the alveoli and ductules are surrounded by contractile basket-like epithelial cells. The ejection of milk from the breast is mediated by neuroendocrine events that culminate in the contraction of those myoepithelial cells. As a result of stimulation of sensory nerves at the nipple and areola during nursing, oxytocin is released from the hypothalamus into the posterior lobe of the pituitary gland and then into the peripheral circulation. Oxytocin triggers myoepithelial cells to contract, forcing milk into the larger ducts and finally through the orifice of the nipple.

Human milk from early in lactation differs from most other external secretions because it contains viable leukocytes. The concentration of leukocytes is highest in colostrum and declines rapidly during the first months of lactation. Table I displays estimates of the numbers of neutrophils, macrophages, and lymphocytes in human milk during the first months of lactation. These numbers are based on morphological characterisitics. However, distinguishing neutrophils from macrophages in human milk is difficult because the morphology of both cells is dominated by the large amount of lipid-containing vesicles in the cytoplasm (Smith and Goldman, 1968 ). The mechanism by which maternal leukocytes enter the milk is poorly understood. However, one potentially important clue to this process is the finding that essentially all these cells have surface markers or physiological features of activated cells. Since most of the surface markers of activation on milk leukocytes are also present on leukocytes found in sites of inflammation, and are known to be important in homing and egress of leukocytes from the vascular compartment, the mechanism of migration of leukocytes into the milk may be similar to that involved in inflammation. Although the array and mechanisms of production of inflammatory mediators in the lactating mammary gland are not well understood, several cytokines that may be involved in leukocyte migration have been detected in human milk, as described in later sections of this chapter. The following sections discuss our current knowledge of the morphology and in vitro function of the milk leukocytes.

Macrophages may have been first photographed in human milk by the French microscopist Alfred Donne (1844). How- ever, little attention was paid to the cells in milk until Smith and Goldman (1968) described milk cells with the morphology and phagocytic activity consistent with activated macrophages. The concentration of macrophages in early milk is usually greater than that of their counterparts in peripheral blood, the monocytes. More recent studies have demonstrated that the milk macrophages are more motile than their counterparts in blood (Özkaragöz et al, 1988; Mushtaha et al, 1989) and display a pattern of surface markers associated with activation (Keeney et al, 1993) . These cells also actively produce toxic oxygen radicals (Tsuda et ah, 1984) . Attributing other activities to the milk macrophages is difficult since most studies of milk leukocytes have used unseparated cells. The role of the milk macrophage in vivo has not been established.

Early in lactation, the concentration of neutrophils in milk approaches that in peripheral blood (Table I) . Neutrophils in human milk have been demonstrated to be phagocytic (Smith and Goldman, 1968) . However, the adherence, response to chemotactic factors, and motility of these cells are less than those of neutrophils from peripheral blood Özkaragöz et al., 1988) . Studies of surface markers suggest that some of these functional features may be the result of prior activation of the neutrophils (Keeney et al., 1993) . Activation of neutrophils may occur during the process of egression from the vascular space, may relate to the process by which large numbers of milk globules are engulfed by neutrophils in milk, or may be the result of exposure to cytokines demonstrated to exist in milk (see subsequent text).

Although the concentration of lymphocytes in human milk is small relative to that in peripheral blood, these cells are consistently present in milk obtained during the first few months of lactation. Approximately 80% of milk lymphocytes are T cells (Wirt et al, 1992) . The precise distribution of T-cell subpopulations in milk lymphocytes is controversial, since different investigators have reported numbers of CD4 + and CD8 + cells similar to those in peripheral blood (Keller et al, 1986 ), a CD8 + -cell predominance (Richie et al, 1982) , or moderate increase in the proportion of CD8 + cells relative to peripheral blood (Wirt et al, 1992) . These differences may be the result of selection of certain subsets during the fractionation of milk or of the analytic limitations of direct fluorescent microscopy. These problems were avoided in the last study by using flow cytometry of unfractionated milk (Wirt et al, 1992) . As in the case for other milk leukocytes, the increased display of certain surface phenotypic markers, including CD45RO, CD25 (IL-2R), and HLA-DR, suggests that the T lymphocytes are activated memory cells (Wirt et al, 1992) .

Milk lymphocytes can be activated to proliferate using mitogens, but their responses are weaker than those of peripheral blood T cells (Parmely et al, 1976; Goldblum et al, 1981) . The spectrum of antigen-specific responses, as measured by proliferation, is thought to differ from that of peripheral blood lymphocytes from the same donor (Parmely et al, 1976) , but the T-cell receptor repertoire of milk T lymphocytes has not been investigated. Although evidence exists for the production of interferon (Emodi and Just, 1974; Keller et al, 1981; Bertotto et al, 1990 ) and monocyte chemotactic factor (Keller et al, 1981) , the full array of cytokines produced by milk cells has not been determined.

In addition to viable cells, several different types of particles are suspended in human milk, including casein micelles, globules packed with lipid, and globular structures containing less lipid but more cytoplasmic structures (Patton and Huston, 1985) . With low speed centrifugation, some of these particles sediment with the cells whereas many of the membrane-bound lipid-filled particles rise to the surface and coalesce. Understanding this particulate structure of milk may be important, since several studies suggest that some host defense factors are compartmentalized within these structures. For instance, centrifugation of human milk causes the concentration of lysozyme to increase approximately fivefold over the value obtained by sampling milk prior to centrifugation (Goldblum et al, 1975) . Crago et al (1979) demonstrated that some of the SIgA antibodies in human milk are contained in lipid-filled particles. Little is known about the direct effects on host defenses of the particles suspended in human milk, although some of them may be neutrophil activators (Keeney et al, 1992) or may interfere with the attachment of enterobacteria to epithelial cells (Schroten et al, 1992) .

a. Immunoglobulins and Ig transport fragments. The major class of immunoglobulins in human milk is Ig A. In contrast, mature cow's milk contains predominantly IgG. The structure and function of SIgA, which makes up at least 80% of the milk IgA, is discussed in Chapters 7 and 11, respectively. Chapter 21 considers the distribution and characteristics of the cells that produce immunoglobulins within the mammary gland. The demonstration of a very high density of IgAland IgA2-producing cells in the lactating mammary gland (Brandtzaeg, 1983) helps explain why human colostrum and milk contain the highest concentrations of SIgA of any secretions. The high proportion of SIgA in human milk of the IgA2 isotype (-40%) relative to plasma (10%) also must be related to the isotype distribution of these cells in the mammary gland. These findings also provide evidence that most of the IgA secreted into the milk is produced locally within the breast, rather than transported from the plasma.

The mechanism of antigenic sensitization and migration of IgA-committed B cells into the mammary gland is considered in several earlier chapters. Briefly, current evidence indicates that many of the IgA antibody responses detected in human milk originate from antigenic stimulation at specialized mucosal sites in the intestinal and respiratory tracts (Goldblum et al, 1975; Roux et al., 1977) . IgA-committed B cells emerging from mucosal sites, such as Peyer's patches in the small intestine, migrate preferentially to other mucosal sites, including the lactating mammary gland. Migration to the mammary gland is under hormonal regulation (Weisz-Carrington et al., 1978) . The wide array of specific antibodies found in human milk suggests that some of these cells are derived from memory B cells rather than from recent antigenic exposure. In the breast, B cells mature into plasma cells, the predominant product of which is polymeric Ig A.

As in other secretory mucosae, transport of immunoglobulins into colostrum and milk is accomplished predominantly by the polymeric immunoglobulin receptor (PIgR). Chapter 10 describes in detail the mechanism by which PIgR mediates specific binding, endocytosis, and transcellular transport of immunoglobulins. Proteolytic cleavage of PIgR at the apical membrane of the mammary alveolar cell releases the polymeric Ig A molecule, covalently complexed to a fragment of PIgR termed secretory component (SC). This complex is called SIgA.

Some of the PIgR molecules are transported and cleaved by the epithelial cells without any attached immunoglobulin. The resulting proteolytic fragment, free SC, is also present in high concentrations in human milk. The function of free secretory component has not been established clearly. One study (Wilson and Christi, 1991) suggests that these molecules may be able to inhibit the enzyme phospholipase A 2 , a function that could reduce inflammatory reactions along mucosal surfaces as well as, perhaps, the fluid accumulation produced by some intestinal pathogens (Peterson and Ochoa, 1989) .

From this brief outline of the immunogenesis of SIgA, we can deduce that this system is well adapted for the production, and secretion into milk, of specific antibodies against pathogenic microorganisms to which the mother's mucosal immune system has been exposed. Since the mother-infant pair normally shares many environmental exposures, this system may be ideal for protecting the infant from potential pathogens entering the environment. As indicated in Chapter 52, several epidemiological studies have shown that the presence in milk of specific SIgA antibodies against enteric pathogens diminishes the incidence or severity of diarrhea caused by bacterial and viral organisms.

Immunoglobulins of the other major isotypes also are found in human milk, although at lower concentrations than in plasma. IgM in milk is in its typical pentameric form, although some of the molecules have noncovalently attached SC, suggesting that IgM is transported into the milk via the PIgR. However, the binding of free SC in milk could generate the same complexes. The antibody specificity of IgM in milk has not been tested extensively, but seems to parallel that of IgA when examined. The presence of IgM antibodies with attached SC should be considered when designing studies of SIgA in human milk, since detection systems based on anti-SC antibodies also may detect secretory IgM (Meilander et al., 1985) .

In cow milk, IgG is the major isotype. However, only small amounts of each of the subclasses of IgG have been detected in human milk. The relative proportion of IgG4 is greater in milk than in serum, suggesting that more of this isotype may be produced locally or selectively transported by the interstitium (Keller et al, 1983) . This hypothesis has not been borne out in a more recent investigation (Mehta et al., 1991) . Nonetheless, the total amount of IgG4 is so low that attributing biological functions to this or the other IgG isotypes will be difficult.

The concentration of IgD in human milk is very low, even relative to serum concentrations (Keller et al., 1984) . IgE is essentially absent from human milk (Underdown et al., 1976) .

Antibodies against a large number of microbes and specific antigens have been detected in human milk. Table II provides a summary of some of these specificities. This list should not be considered complete or thought to imply functional significance of the presence of antibodies of particular specificity, since it respresents a summary of studies from groups with particular interest in the antigens tested.

The stability of the immunoglobulins in human milk has been the subject of a number of studies, most of which have concentrated on SIgA. The majority of the IgA molecules in postnatal milk seems to be intact, based on Western blots using anti-á chain antibodies as developing reagents (Cleveland et al., 1991) . Thus, during active lactation, little degradation must occur within the mammary gland. Following the fate of the SIgA within the infant is difficult. Fecal excretion of SIgA has been examined in low birth weight and full-term infants (Schanler et al, 1986; Prentice et al, 1987; Davidson and Lönnerdal, 1987) . The finding that SIgA excretion in the feces was 30 times higher in low birth weight infants receiving human milk than in similar infants fed cow milk formulas strongly suggested that a portion of the ingested milk survived the whole gastrointestinal tract. However, when expressed as a proportion of the SIgA fed, approximately 9% of the SIgA was recovered as SIgA (Schanler et al., 1986) .

The function of mucosal immunoglobulins is discussed in detail in Chapter 11. Of potential importance for milk immunoglobulins is the amplification of the effect of other milk defense factors by Ig A. For instance, some of the lactoferrin in milk is found complexed with Ig A (Arnold et al., 1977) . These complexes may have enhanced activity since they can be targeted to surfaces of pathogenic microorganisms where lactoferrin could function to chelate selectively the iron needed by the microorganism for growth. Microorganisms that are resistant to the lytic action of lysozyme may become more susceptible in the presence of SIgA and complement (Adinolfi et al., 1966) . Galactosyltransferase enzyme also complexes tightly with Ig A, although the functional significance of these complexes is not known (McGuire et al., 1989) .

b. Lysozyme. Lysozyme, a 12-kDa single polypeptide, catalyzes the hydrolysis of ßl-4 linkages between Nacetylmuramic acid and 2-acetylamino-2-deoxy-D-glucose groups in bacterial cell walls, leading to direct lysis of susceptible bacteria, predominantly those without an extensive cell wall. As indicated earlier, interaction with IgA and complement may expand the antimicrobial range of activity of this secretory enzyme.

The quantity of lysozyme supplied to the infant each day are presented in Table III . Although the concentration varies during lactation the amount delivered appears to remain relatively constant for at least the first 4 months (Butte et al., 1984) . These concentrations are among the highest of any secretion (Jolles and Jolles, 1967) .

The relative stability of lysozyme against acid denaturation and tryptic digestion makes it well suited to function in the gastrointestinal tract of the recipient infant. However, the fate of the ingested lysozyme is not clear. Low birth weight infants who are fed human milk excrete about eight times more lysozyme in their stool than do cow milk-fed infants (Schanler et al., 1986) .

Lactoferrin is the whey protein with the highest concentration in human milk. The daily amount of lactoferrin ingested by the infant at various stages of lactation are shown in Table III . A gradual decline is seen in the amount transferred to the infant, beginning soon after initiation of lactation.

A single chain glycoprotein of 79 kDa, lactoferrin consists of two globular lobes, each with two domains surrounding a binding cleft for an atom of ferric iron and a bicarbonate ion. The major function of lactoferrin is the chelation of iron. In that respect, apolactoferrin robs the siderophilins of microorganisms of iron that is essential for their growth (Spik et al., 1978) . The lactoferrin in human milk is well suited for this role, since 90% of the molecules are devoid of iron (Fransson and Lönnerdal, 1980) . Several other functions have been suggested for lactoferrin. The finding of a specific receptor for lactoferrin on the mucosa of the upper bowel suggested that lactoferrin might enhance the uptake of milk iron by the infant (Davidson and Lönnerdal, 1988) . The low degree of iron saturation in milk lactoferrin makes this function seem unlikely, unless iron was transferred from other compartments during the digestion process. Some evidence also suggests that lactoferrin has trophic effects on enterocytes (Nichols et al., 1987) and may inhibit complement activity (Kijlstra and Jeurissen, 1982) .

Few studies have been done on the disposition of milk lactoferrin in the infant. One study was carried out on infants with enterostomies, which allowed the gut contents to be recovered before entering the colon (Hambreus et al., 1989) . The results indicated that 9-32% of the ingested lactoferrin could be recovered from this site. Low birth weight infants fed a human milk preparation excreted almost 200 times more lactoferrin in their stool than similar infants fed a cow milkbased formula (Schanler et al., 1986) . However, only 3% of the ingested lactoferrin was recovered in the fecal sample. In addition, a major portion of the excreted lactoferrin was partially digested, resulting in molecules of unknown activity (Goldman et al., 1990) . Infants fed human milk also had a larger amount of lactoferrin and lactoferrin fragments in their urine (Goldblum et al., 1989) ; the molecular sizes of those fragments were similar to those in the stools (Goldman et al., 1990) . Another study using stable isotope methods also suggested that some lactoferrin derived from the milk may a Data modified from Butte et al. (1984) .

be absorbed intact from the intestinal tract and then excreted into the urinary tract (Hutchens et al, 1991) . If this occurs, the absorbed lactoferrin must be cleared rapidly since human milk ingestion does not increase the serum concentration of lactoferrin (Schanler et al., 1986) .

Many of the components of the classical and alternative complement pathway have been detected in human milk (Ballow et al., 1974; Nakajima et al., 1977) . However, with the exception of C3, the concentrations of these factors are very low. The activity of the complement system in human milk is not likely to be great, although interactions with other milk constituents may allow some function (Adinolfi et al., 1966) .

e. Bioactive peptides. Several cytokines have been quantified by immunoassays in human milk, including interleukin-lß (IL-lß; Munoz et al., 1990) , tumor necrosis factor a (TNF-a; Mushtaha et al, 1989; Rudioff et al., 1992a) and IL-6 (Saito et al, 1991; Rudioff et al, 1992b) . The functions of these factors in the infant remain to be elucidated. However, studies of the leukocytes in the milk suggest that some of these cytokines may be active (Söder, 1987; Mushtaha ei a/., 1989) . Of special interest is the finding that incubation of peripheral blood leukocytes with human milk causes monocytes and neutrophils to become activated. Further, addition of neutralizing antibodies against human TNFa abrogated the activating effects of milk on monocytes (Mushtaha et al, 1989) . Some fragments of casein, the ß-casomorphines, which are created during proteolysis of casein in the gastrointestinal tract, are biologically active (Teschenmacher, 1987) . ß-Casomorphines not only have endorphin effects but may be immunoregulatory as well (Parker et al, 1984) .

Several different isoforms of prolactin have been demonstrated in human milk that apparently are produced by posttranslational modifications in the mammary gland. Although the function of each of these isoforms is not delineated, the basic protein molecule has been found to influence the development of T cells in animal model systems (Chikanza and Panay, 1991; Gala, 1991; Rovensky et al,\99\) and to enhance the formation of specific antibodies in serum and milk (Ijaz et al, 1990) .

The array of growth factors in human milk includes epidermal growth factor (EGF), insulin, transforming growth factor ß (TGF-jS; Hooton et al, 1991) , and mammary gland derived growth factor (Kidwell et al, 1987) . Some of these factors have been postulated to aid in the postnatal development of the mucosal barriers of the intestinal and respiratory tracts. However, the in vivo effects of these factors are not well characterized.

a. Lactobacillus growth factors. Human milk contains high levels of a growth-promoting activity for Lactobacillus bifidus var. Pennsylvania (György et al, 1974) . This activity, which is essentially absent from cow milk, is generated by oligosaccharides (György et al, 1974) , glycopeptides, and proteins (Nichols et al, 1975; Bezkorovainy et al, 1979) .

Similar activity associated with caseins also may be the result of oligosaccharide moieties on that protein (Bezkorovainy and Topouzian, 1981) . The role of these factors in host defense may be related to the predominance of Lactobacillus in the bacterial flora in the colon of infants fed human milk. The large amount of acetic acid produced by these organisms suppresses the growth of enteropathogens.

b. Oligosaccharides and glycoconjugates. Human milk is rich in oligosaccharides that appear to be formed in the mammary epithelium by the same galactosyltransferases that glycosylate proteins and peptides, using lactose as the acceptor molecule. Various biological activities have been attributed to the whole group of oligosaccharides (Holmgren et al, 1981) and, more recently, to individually characterized moieties, including fucosylated oligosaccharides that inhibit the hemagglutinin activity of the classical strain of Vibrio cholerae and protect against the heat-stable toxin of Escherichia coli (Newburg et al, 1990) . Mannose-containing glycoproteins and glycolipids interfere with the fimbria-mediated binding of E. coli (Holmgren et al, 1987; Wold et al, 1990) . The attachment of Haemophilus influenzae and Streptococcus pneumoniae to epithelial cells is inhibited by saccharides containing the disaccharide subunit Af-acetylglucosamine (l-3)-ß-galactose (Andersson et al, 1986) . These units may exist as free oligosaccharide or in glycoproteins or peptides. In any case, molecules with these structures may act as false receptors for the lectinlike adherence structures on the microorganism and thereby protect the infant from colonization or infection with these pathogens. Although an in vivo role for these oligosaccharides is suggested by animal models (Otnaess and Svennerholm, 1982; Cleary et al, 1983; Ashkanazi et al, 1992) few human studies have been done that pertain to this question.

a. Unsaturated fatty acids and monoglycerides. Free fatty acids and monoglycerides are produced by the digestion of milk triglycerides by bile salt-stimulated lipases or lipoprotein Upases in human milk. In addition, the lingual and gastric lipase activities of the recipient infant are active on the milk triglycerides (Hosmosh, 1990) . The lipid products have several host defense activities including disruption of enveloped viruses (Stock and Frances, 1940; Welch et al, 1979; Issacs et al, 1986; Thromar et al, 1987) , which may prevent coronavirus infection in the intestinal tract (Resta et al, 1985) . The fatty acids and monoglycerides also may provide some defense against intestinal parasites such as Giardia lamblia (Gillin et al, 1983 (Gillin et al, ,1985 Herneil et al, 1987) .

b. á-Tocopherol and /3-carotene. Two vitamins found in human milk (Chapell et al, 1985) also may have host defense activity. High levels of á-tocopherol in milk may serve as an antioxidant, but additionally this vitamin is known to stimulate the development of immunity (Tengerdy et al, 1981; Bendich et al, 1986) . ß-Carotene, another potent antioxidant, is present in high concentrations in the mammary gland at parturition. This agent is released from the tissue into milk during the first few days of lactation (Chapell et al., 1985) . As a result of the ingestion of á-tocopherol and ß-carotene in human milk, the blood levels of these two agents rise substantially in the recipient infant (Chapell et al., 1985; Ostrea et al., 1986) . These and other agents in human milk may regulate inflammatory responses and immune functions of the infant.

Despite the identification and quantification in human milk of many factors that have the potential to protect the lactating breast and the recipient infant, little currently is known about how these factors function in vivo. Progress in this area has been limited by the types of studies that can be carried out in human infants and by the large species differences in milk composition and function that make experimental animal studies difficult to apply to humans. However, certain patterns of factors may provide clues to unique in vivo function of human milk.

In contrast to many mucosal glands, which function on a continuous basis, the mammary gland secretion of immune factors is restricted largely to periods of lactation. The factors that regulate the onset, quality, and quantity of the human milk are only partially understood. Prolactin and other lactogenic hormones are essential for the onset and maintenance of lactation. An array of growth factors including EGF, insulin, and mammary gland derived growth factors that are concentrated in human milk (Kidwell et al., 1987) also may play a role in these processes.

The same proximity of the mucosal surfaces to the external environment that leads to extensive exposure to microorganisms and other antigens allows the mucosal immune system to defend against infections without the need for the extensive inflammatory and phagocytic responses that are typical of the systemic defenses. Thus, if factors in milk can reduce the adherence, colonization, or growth of microorganisms in the infant's respiratory or intestinal tract, the incidence or severity of infection would decrease correspondingly without producing much physiological abnormality in the infant. We have hypothesized previously that a characteristic of the immune system in human milk is the absence of phlogistic factors and the presence of agents with anti-inflammatory activity . Demonstrations that infants who receive mother's milk that contains specific antibodies against an enteric pathogen still have culture-proven infections but less diarrhea than those receiving milk without those antibodies (Glass et al., 1983 ; also see Chapter 52) are in keeping with this hypothesis. In that respect, the lower morbidity of breast-fed infants infected with rotavirus was not found to be related to the levels of specific antibodies in the milk (Duffy et al., 1986) . This result suggests that other agents, including anti-inflammatory factors, may be responsible for some of the protection against certain pathogens.

Several studies suggest that breast feeding may have effects that last much longer than the breast-feeding period. For instance, breast-fed infants have a lower incidence of juvenile diabetes mellitus (Mayer et al., 1988; ) and Crohn's disease (Koletzko et al, 1989 ) than those fed formulas. Retrospective analysis also suggests a diminished risk of lymphomas after breast-feeding (Davis et al., 1988) . Whether these long-term effects are the result of mucosal immune factors in human milk is unclear. However, speculating that breast-feeding alters the development of the infant's immune system or protects against certain infections during a critical developmental period, thereby preventing illnesses that become manifest later in life, is interesting.

Serological properties of TJA antibodies to Escherichia coli present in human colostrum

Inhibition of attachment of Streptococcus pneumoniae and Haemophilus influenzae by human milk and receptor oligosaccharides

A bactericidal effect for human milk lactoferrin

The effect of human milk on the adherence of enterohemorrhagic E. coli to rabbit intestinal cells

Developmental aspects of complement components in the newborn. The presence of complement components and C3 proactivator (properdin factor B) in human colostrum

Dietary vitamin E requirement for optimum immune responses in the rat

Human breast milk T cells display the phenotype and functional characteristics of memory T cells

Bifidobacterium bifidus var. pennsylvanicus growth promoting activity of human milk casein and its derivatives

Isolation of a glycopeptide fraction with Lactobacillus bifidus subspecies pennsylvanicus growth-promoting activity from whole human milk casein

The secretory immune system of lactating human mammary glands compared with other exocrine organs

Daily ingestion of immunologic components in human milk during the first four months of life

Vitamin A and E content of human milk at early stages of lactation

Hypothalamic-pituitary mediated modulation of immune function: Prolactin as a neuroimmune peptide

Protection of suckling mice from the heat-stable enterotoxin of Escherichae coli by human milk

Characterization of secretory component in amniotic fluid: Identification of new forms of secretory Ig A

Human colostral cells. I. Separation and characterization

The persistence of human milk proteins in the breast-fed infant

Specific binding of lactoferrin to brush-border membrane: Ontogeny and effect of glycan chain

Infant feeding in childhood cancer

Cours de Microscopie

Modulation of rotavirus enteritis during breast-feeding

Interferon production by lymphocytes in human milk

Iron in human milk

Prolactin and growth hormone in the regulation of the immune system

Human milk kills parasitic protozoa

Cholatedependent killing of Giardia lamblia by human milk. Infect. Immun

Protection against cholera in breast-fed children by antibodies in breast milk

Antibody forming cells in human colostrum after oral immunization

Human milk banking I. Effects of container upon immunologic factors in mature milk

Human milk feeding enhances the urinary excretion of immunologic factors in low birth weight infants

Immunologic factors in human milk during the first year of lactation

Anti-inflammatory properties of human milk

Molecular forms of lactoferrin in stool and urine from infants fed human milk

Undialyzable growth factors for Lactobacillus bifidus var. pennsylvanicus

Lactoferrin content in feces in illeostomy-operated children fed human milk

Reduced risk of IDDM among breast fed children. The Colorado IDDM Registry

Lingual and gastric Upases

Killing of Giardia Lamblia by human milk lipases: An effect mediated by lipolysis of milk lipids

Nonimmunoglobulin fraction of human milk inhibits bacterial adhesion (hemagglutination) and enterotoxin binding of Escherichia coli and Vibrio cholerae

Receptor-like glycocompounds in human milk that inhibit classical and El Tor Vibrio cholerae cell adherence (hemagglutination)

Inhibition of bacterial adhesion and toxin binding by glycoconjugate and oligosaccharide receptor analogues in human milk

Human colostrum contains an activity that inhibits the production of IL-2

Origin of intact lactoferrin and its DN A-binding fragments found in the urine of human milkfed preterm infants. Evaluation of stable isotopic enrichment

Neuroimmunomodulation of the in vivo anti-rotavirus humoral immune response

Membranedisruptive effect of human milk: Inactivation of enveloped viruses

Human tear and human milk lysozymes

Activated neutrophils and nutraphil activators in human milk: Increased expression of CD11B and decreased expression of L-Selectin

Lymphokine production by human milk lymphocytes

Local production of IgG4 in human colostrum

IgD-A mucosal immunoglobulin?

T cell subsets in human milk

Production of growth factors by normal human mammary cells in culture

Modulation of classical C3 convertase of complement by tear lactoferrin

Role of infant feeding practices in development of Crohn's disease in childhood

A human milk galactosyltransferase is specific for secreted, but not plasma

Reduced risk of IDDM among breast fed children

Immunoglobulin G subclasses in human colostrum and milk

Secretory IgA antibody response against PYexcheria coli antiens in finfants in relation to exposure

Composition and properties of submicellar casein complexes in colloidal phosphate-free skim milk

Milk membranesorigin, content, changes during lactation and nutritional importance

Interleukin-1/3 in human colostrum

Chemokinetic agents for monocytes in human milk: Possible role of tumor necrosis factor-á

Complement system in human colostrum

Fucosylated oligosaccharides of human milk protect suckling mice from heat-stable enterotoxin of Escherichia coli

Human lactoferrin stimulates thymidine incorporation into DNA of rat crypt cells

Isolation and characterization of several glycoproteins from human colostral whey

Influence of breast-feeding on the restoration of the low serum concentration of vitamin E and 0-carotene in the newborn infant

Non-immunoglobulin fraction of human milk protects against enterotoxin-induced intestinal fluid secretion

The motility of human milk macrophages in collagen gels

Immunostimulating hexapeptide from human casein: Amino acid sequence, synthesis, and biological properties

In vitro studies on the T-lymphocyte population of human milk

Human Lactation: Milk Components and Methodologies

Role of prostaglandins and cAMP in the secretory effects of cholera toxin

The nutritional role of breast milk IgA and lactoferrin

Isolation and propagation of a human enteric coronavirus

Distribution of T lymphocyte subsets in human colostrum

Origin of IgA-secreting plasma cells in the mammary gland

Evidence for immunomodulation properties of prolactin in in vitro and in vivo situations

Tumor necrosis factor-á in human milk

Interleukin-6 (IL-6) in human milk

Detection of IL-6 in human milk and its involvement in IgA production

Enhanced fecal excretion of selected immune factors in very low birth weight infants fed fortified human milk

Inhibition of adhesion of s-fimbriated Escherichia coli to buccal epithelial cells by human milk fat globule membrane components: A novel aspect of protective function of mucins in inoimmunoglobulin fraction

The cells of human colostrum. I. In vitro studies of morphology and functions

Isolation of interleukin-1 from human milk

Bacteriostasis of a milk-sensitive strain of Escherichia coli by immunoglobulins and iron-binding proteins in association

The inactivation of the virus of epidemic influenza by soaps

Vitamin E, immunity and disease resistance

Human Lactation 3: The Effects of Human Milk on the Recipient Infant

Decreased response of human milk leukocytes to chemoattractant peptides

Inactivation of enveloped viruses and killing of cells by fatty acids and monoglycerides

Oxygen metabolism of human colostral macrophages

The relative paucity of IgE in human milk

Hormonal induction of the secretory immune system in the mammary gland

Effect of antiviral lipids, heat, and freezing on the activity of viruses in human milk

Activated-memory T lymphocytes in human milk

Gravidin, an endogenous inhibitor of phospholipase A2 activity, is a secretory component of Ig A

Secretory IgA carries oligosaccharide receptors for Escherichia coli type 1 fimbrial lectin